PSI - Issue 42

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Author name / Structural Integrity Procedia 00 (2019) 000 – 000

Rui F. Fernandes et al. / Procedia Structural Integrity 42 (2022) 1054–1060 © 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of 23 European Conference on Fracture - ECF23 Keywords: Fatigue crack growth; Laser powder bed fusion; Heat treatment;

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1. Introduction Additive manufacturing (AM) allows the production of complex shapes based on 3D CAD files ensuring a simpler process when compared with conventional methods, due to the layer-by-layer strategy. Besides that, with this strategy it can be explored the geometry optimization based on the 3D printing potential that leads to the weight reduction of the component. Laser Powder Bed Fusion (LPBF) is a process within additive manufacturing that enables the use of powders to produce metallic components. Regarding this, the aluminum alloys have a huge relevance linked to this process due to the good properties, as good weldability, low density, high strength, and excellent oxidation and corrosion resistance (Wu et al. 2016; Yan et al. 2019). The ability to produce complex shapes and lightweight metallic components make this process an innovative opportunity for the aerospace and automotive industries that are always requiring lighter optimized components. However, the behavior of LPBF components under demanding loads needs to be well analyzed to avoid fatigue failures. As it is well described in literature, this process introduces some defect like pores, lack of fusion, residual stresses and high surface roughness, that have a major impact in the fatigue lifespan of the components (Yang et al. 2018; Brandão et al. 2017). Different suggestions have been investigated to improve fatigue resistance of this alloy. Regarding post-treatments the main LPBF machine producers recommend applying T6 (temperature higher than 500ºC) and stress relief (270 300ºC) heat treatments. However, these heat treatments show a huge influence in the strength of the AlSi10Mg alloy, when compared to the as-built state (GmbH 2014; Tridello et al. 2019). Uzan et al. ( 2017) has studied the influence of HIP treatment at 500ºC in the mechanical properties and the strength of the material was also affected by the high temperature treatment. Regarding the microstructural changes motivated by the application of the heat treatments, Fiocchi et al. (2021) have conclude that the application of heat treatments with temperature above 260ºC will contribute to the Si precipitation from the supersaturated Al matrix, which it will lead to a decrease in the mechanical properties. Thus, in this paper will be analyzed the fatigue crack growth (FCG) performance of AlSi10Mg alloy in the as-built (AB) state and with two distinct heat treatments with temperatures below 260ºC. Regarding FCG results, Giovanni et al. (2019) have tested the specimens in two different states with different orientations: AB and with T6 heat treatment and conclude that the heat treatment was responsible for a microstructural and residual stresses homogenization that lead to a minimization of the effect of the building orientation. Besides that, the heat-treated samples have reached low crack growth rates (da/dN) for the same ΔK . Macías et al. (2021) have studied the effect of the stress relief heat treatment at 300ºC also in the FCG and the heat treatment shows a reduction in the crack growth rates. However, the application of these heat treatments shows worst performance in the fatigue strength of the material, when compared to AB state (Macías et al. 2021; Chen et al. 2018). The main goal of this work is to study the FCG behavior of the material, with two non-standard heat treatments different from those in the literature and understand the difference between them and the as-built state.

Nomenclature 3D

Three-dimensional space

AB AM CT FCG HIP

As built

Additive manufacturing Compact tension Fatigue crack growth Hot isostatic pressing